Power line carrier frequency telephone system



July 25, 1950 R. c. EDsoN ETAL POWER LINE EARRIER FREQUENCY TELEPHONE SYSTEM Filed Aug. 22, 1946 /NvEA/rons:

ry. N m T T A July 25, 1950 R. c. EDsoN Erm.

PowER LINE CARRIER FREQUENCY TELEPHoNE SYSTEM Filed Aug. 22, 1946 4 Sheets-Sheet 2 ATTORNEY R. C. EDSON ETAL July 25, 1,950 2,516,763

POWER LINE CARRIER FREQUENCY TELEPHONE SYSTEM Filed Aug. 22, 1946 4 Sheets-Sheet 3 July 25, 1950 R. c. EDSON m. 2,516,763

POWER LINE CARRIER FREQUENCY TELEPHONE SYSTEM Filed Aug. 22, 1946 4 Sheets-Sheet 4 COUPLE R f 'fs-0% BV UE O. @me

ATTORNEY transmission line.

Patented July 25, 1950 l'L JNILED STATES PATENT u v,ol-Flclszj POWER LINE CARRIER FREQUENCY TELEPHONE SYSTEM ted, New York, N. YL, a corporation of New York Application August 22, 1946, Serial No. 692,350

16 Claims.

This invention relates to communication systems and particularly to telephone systems including subscribers stations arranged for carrier current operation over a power transmission line. v Objects of the invention are the provision of carrier telephone service over power transmission lines, the provision of means for automatically marking the telephone lines which connect the vpower lines to, a telephone central oflice busy on calls between telephone stations connected to the power lines, the elimination of manual control- :ment of power line carrier telephone systems.

Y l This invention embodies a telephone system in which a subscriber line terminating in a, telephone y central ofce of the system is common to a group of subscriber stations, each of which is connected to, and arranged for carrier current operation over, a transmission medium such as a power from the central o'ice with the power transmission line. A first carrier frequency is used for the transmission of speech and signals from the .central oilice over the power line to a calling or v:called one of these carrier subscriber stations; a

second carrier frequency is used for the transmission of speech and signals from any one of the Acarrier stations to the central office and for the transmission of speech from a called one of the carrier stations on calls between stations of the group; and a-third carrier frequency is usedvfor v.the transmission of .speech from a calling carrier station to the called carrier station on calls between stations of the group.

, `A feature of the invention is the provision of means in carrier terminal equipment which interconnects a power transmission line and a tele: phone line from a telephone central office, for applying divided code ringing to the group of carrier telephone stations associated with the telephone line.

According to this feature the arrangement is such that some of the stations are signaled by ringing current transmitted on posil Another ieature'of the invention is the use of 'relaxation oscillators for controlling the application .of energizingpotential togthecarrier trans-l A carrier terminal equipment2 'gunit isprovided for connecting the subscriber line .l5 for applying semi-selective ringing to the stations, .and in general the simplification and improvemitter at the carrier terminal, the operation of each of these oscillators being so controlled that the carriertransmitter is energized every second, third, ,or other chosen integral submultiple positive half cycle of the power wave or every second, third, or other chosen integral submultiple negative half cycle of thepower wave, depending upon whether the ringing current is received at the carrier terminal equipment over the tip conductor or `over the ring conductor of the telephone line from the telephone central ofi-ice.y

A clearl and complete description of the invention will be facilitated byconsidering a system in which the invention and its features are embodied, such a system `being represented schematically in the drawing. The invention is, however, not limited in its application to the particular system shown but is generally applicable to telephone systems.

The drawing, which consists of six figures, represents an automatic telephone exchange serving subscriber stations, some of whichare arranged for carrier current operation over a power transmission line.

Fig. `1 shows an automatic telephone exchange comprising a subscribers lstation IIl, subscribers 4lines, II and 2|, and line circuits I2 and 22, linender switches LFI and LFZ, selector switches SI and SI2, and connector switches CI. and C2.

Fig. 2 shows carrier terminal equipment CEI individual to the line 2 I a power generator G, and

a power transmission line PL to which the carrier terminal equipment CEI is coupled by coupling meansIIl'l;`

. Fig. 3 shows one of a plurality of subscribers stations `connected to and arranged for carrier current operation over power line PL.

. Fig. 4 shows the relative position of Figs. 1 to 3 to form an operative arrangement;

Fig. 5 shows carrier terminal equipment CE2 arranged for lfour-party selective or eight-party semi-selective ringing; and

Fig. 6 shows the kind of ringing and oscillator apparatus involved in ringing each of eight stations associated with the terminal shown in Fig. 5.

The subscribers station III is of the usual type Iprovided. for use on lines terminating in an automatic central oice and includes a dial or other impulse sender (not shown) for use in selectively controlling the switches throughl which desired connectionsfare established. The line-nder, selector and connector switches may be of the twomotion, step-by-step type.l Each of the linender `and selector switches is represented in the drawing by a set of brushes and a single set of terminals and each of the connector switches is represented by a set of brushes and two sets of terminals. The relays and other apparatus associated with the line-under, selector and connector switches are represented by broken lines. Reference may be had 4to Automatic Telephony, by Smith and Campbell, second edition, V'pages "53 to 65, inclusive, for a detailed description of the structures of such switches and their operation when used as selectors and connectors. iReference may be had to the patent to R. L. v`Stolrely, No. 1,799,654, granted April 31, 1931, for a detailed disclosure of a line circuit aiii'a'line-nd'er of the step-by-step type. The ringing codegenferator 21 comprises a source of ringing current and means for interrupting the ringing supply conductor as required to produce Laiplurality-m? 'Idif' ferent ringing codes for signaling subscribersstations. Reference may fbe had to the patent to -Duguid, No. 2,225,907, granted December 24, 1940, yfor'a `disfclb`sure of such-a'ri'ii'ging code .generator and to "the patent jt@ "Koechling, No. 2,289,503, kgranted July 1'4, 19'42ffo'r a 'detaiied'uiscmsure'of a connector switch 'arranged "for ten-party'code ringing.

The carrierter'minal equipment CEI comprises a carrier 'current tr'ansmitterlfCTL two carrier current receivers CRI and CE2, a hybrid coil or group of "transformer windings "HC'anda network '3'4 arranged to 'transmit signal and 'Voice currents to and from line "2|, 'ringing relays 5I and' I, two relaxation oscillators OT and 0R, relays M, 42,4, j'115 'fand "41, and 'a' power transformer PTI v't'.o'g'ether with other "pieces of `apparatus including ilters, rectifiers, condensers andrsista'nces. Themid'dle left pairof windings '30 Jofthe -hybrid coil HC "are connected by normally openco'nta'cts'of a control relayZ to the conductorsof line "21; "andthe clos'u're'of 'a directV current circuit 'through 'these windings in series with 'line 2'I 'is under the *control of vrelay Y35`is provided for connection in place` of the bal- /voi'c'e 'frequency currents from the "'carrier receiv'erbCRl land the 'lower "pairoi winding 32 of the hybrid coil transmit *voice Lfrequency cur- G'50 rent fro'mli'n'e ill `to the carriertransmitter-'CTI vTheparrier `receiver CRI comprisesna receiving :filter IBL tunedlto receive voice modulatedand signal modulated carrier currents of a frequency F2over/the powerfline from any onevdfthecar rier subscriber 'telephone stations associated therewith, `an amplifier VI'll'2 and vde'modulators I 05 and I 0B. 'Ihecarrier ireceiver CR2 A:comprises a receiving filter 'm1, "tuned to lreceive carrier Vcurrent of afrequency 113 transmittedover'fthe 4power Vline on a "reverting call from Ythe calling one of the carrier stationsan'amplifier 4I'IllLand a demodulator 199. y

The carrierA transmitter CTI comprises an `oscillator-modiilator tube 8U and an amplifier which is determined by "crystal '584. Since -voice 4rie'rjfrequency -FI The tuned circuit has v`aflfiigh l70' 'impedanceat frequencies other than-that of Athe crystal 84 vso as to prevent A'oscillationat frequencies other than the desired carrier frequency mitted to tube through the lower pair of windings 32 of hybrid coil HC, the output current of tube 80 includes both modulated carrier and voice frequency components. The elements S6 and have a high impedance at the carrier fre- 4quencyand a flowfimpedance at voice frequencies; and element 94 has a low "impedance at v'the carrier frequency and at voice frequencies. The 'voice modulated carrier frequency output of tube 80 is impressed through condenser 91 on the control .-grid of amplier tube 98; and the amplied carrier current is transmitted through transformer "99, condenser IUD and coupler Illl over "the .power line PL. The energy for operating `tubes'i'l] Vand 98 vand for operating the vacuum tubes of the carrier receivers CRI and CR2 is obtained from the power line through a transformer PTI. Plate current for the vacuum tubes is supplied through part of winding 14 of transformer PTI, rectifier 15, lter 16, and conductor '11. Winding '14 also Isupplies alternating -voltage 'to the upper -element of each of tubes v`"51 and- 61 o'f :the relaxationr oscillators fto vfcontrol the 'transmission of Aringing signals over Althe -power line to the 'carrier subscriber stations as "hereinafter "further described. AWinding Il sof =power transformer PTL in combination withrectiers 12, constitutes va source of negative potential i'for 4operating relays 42 'and I444, and 'for t"biasing `the vgrid "of :tube 518. The -laments yof Itubes 80 'and $58 are 'heated by energy transmitted through 'windings I19 and "18 of lpower trans'former"-P'1l these windings being shown adjacent the tub'es. Other windings of pOWer-tranSOrnierP'DIsupply -the `current 'for heating the -iilaments l-of fthe vacuum :tubes 'of fthe carrier `IreceiversCl'JI and CR2. The 'carrier receivers Aare normally -en'ergized `ready `to 4receive r`signals vbut the bias inorvrnally provided for tubes 80 andSB is such `-that 'there Lis normally substantially 1noeurrerit in ithe plate circuits of *these-times.` When fthe'transmiss'ion :jf-carrier current of frequen'cy IFI Iyis desired, the operation of one 'of relays i412, 5| and -(il'short"circuits biasing resistor 69 'to decrease the negative fbias on the gridfo'f tube 580; ianii lthe 'operation of relay 342i'or -the break-downff either one'of gas-filled tubes '251l and f B1 decreases the negativebiasiof --tube @8 'l to 'increase 2the fout- -putofithe amplifier. The-'operationi-ofthe car- 'rier lterminaliequipment CE I of Figi 2 'is liereinafter further f described f on calls to and from the carrier Isubscriber stations.

Eachof the' carrier subcriber stations? comprises la carrier receiver CRiL'aA carrier transmitterfCT3, a telephone ha'ndset |15 consisting fof a receiver |16 and transmitter *111, `la dial I-'TU lfor userin establishing `connections 'through f the central l of- 'ce, '2a ringer |56, `relays ISU 'and T61); and llpower supply smeans Vcomprising a i power 4transformer PTS. The carrier receiverCR3,'comprisesffilter units'FI'Zf and'FlZS which'-t transmit currentof-carrier 'frequency TFI "and vsuppress feomponents of other frequencies, y'a earrierffrequency1amplifler 'tube |25,- an -interstage -ilter F1214, another 'Tamplilier tube l3i2,'an outputiilter FLISand "a-'Idemodulator I `41. 'The vvoice'frequenoy component `of the output'offdemodulato'r '|41 operates l-tlie ftlephcne receiver I1B andftliedirect'currenticomp'onent of the output of demodulator z-Il1contrcls relay ISU. .fAutomaticfcontrol of the gaino'f tube |525 =-is provided i from rectifier TMI of ylter 'iunit 5:1135. The carrier 'l'transmitter lC'I13 includesaI transfrmer l'HiB;"connecting` theiteleplionetrans- `reoluenc'y current'fr'om' telephone line 2 Iisftrfans- 175 andi mdulatortll', andiincludesitwoicrystalsi2 and |63 for Econtrolling the frequency ofthe-car#- frequency F2 and crystal |63 oscillates at the carrier frequency F3. Relay |60 switches the crystals |62 and |63. Winding I8I of power transformer PT3 supplies the energy for heating the filament of tube'v I 25.; and other windings (not shown) supply the current for heating the filament of tube |32 and the filaments of the vacum tubes of the carrier transmitter GT3. Winding |85 in combination with rectifier |90 supplies through conductor |93 the current for the plate circuits of all of the vacuum tubes at the subscriber station, and also the current for actuating ringer |56 and relay I60. Winding |85 also supplies alternating voltage tothe screen grid of tube |32 for divided ringing control as hereinafter further described. The switch |14 associated with the receiver hook controls the energization of the carrier transmitter CT3 but the carrier receiver CR3 is continuously energized ready to respond to incoming signals.

Call from central ojce to carrier subscriber station Assume now that a call is initiated at a subscriber station I0, that a line finder LFI is operated to extend a connection from station III over vline II to the first selector SI, that selector SI is selectively operated responsive to the dialing of the first digit of the called subscribers directory number by the calling subscriber at station I6, that the selector SI extends the connection to an idle connector switch CI, and that the connector CI is selectively controlled by the dialing of the last digits of the called subscribers directory number to select the called line and to select the particular ringing code with which the called subscriber is signaled. Assume further that the called station is one of the carrier subscriber stations associated with carrier terminal CEI and telephone line 2|. A busy test of the line 2| is made and if the line tests idle, ringing current is transmitted over line 2 I. switch may be arranged for either divided code ringing or bridged code ringing it will be assumed that the connector is arranged for divided code ringing; and the carrier terminal equipment CEI `and carrier subscriber stations shown in Figs. 2 and 3 are shown arranged for divided code ringing. The ringing current frequency may be 20 cycles per second and relays 5| and 6| are of a type which will operatively respond to current of such a frequency. If the called station is signaled over the tip conductor of line 2|, the ring- A ing current effects the operation of relay 5| of the carrier terminal equipment CEI during each ringing interval of the selected ringing code; and, if the called station is signaled over the ring conductor of line 2|, the ringing current e'ects the operation of relay 6| of the carrier terminal equipment CEI during each ringing interval 'of the selected ringing code. The operation of either relay 5| or relay 6|, responsive to ringing current transmitted over line 2|, closes a short circuit across resistor 89 thereby reducing the grid bias of oscillator tube 80 of carrier transmitter CTI. The operation of relay 5I connects the' plate supply conductor 11 to relaxation oscillator OT and the operation of relay 6| connects the plate supply conductor 11 torelaxation oscillator OR. The two relaxation oscillators OT and OR are made up of, similar elements and operate in like manner. Assume that relay 5I 'isoperatedby they Although the connector ringingcurr'ent received over `line 2|V from con nector CI. The operation of'relay 5| closesal circuit-for charging condenser 56, this circuit being traced from plate supply conductor.11, through a front contact of relay 5|, resistors 52 and 55,' condenser 56, resistor 59, conductor .10, winding 1I of power transformer PTI and rectiers 12 to ground. The charging of `condenser 56 ybuilds up a voltage across the control gap of gasiilled tube`51, a predetermined interval of time being required to charge condenser 56 to a voltage sufficient to ionize the controlgap of tube 51. As soon thereafter as the winding 14 of power trans,- former PTI is energized in a direction where ren,- ders the main anode of tube 51 positive with respect to ground potential, a discharge is started between the main anode and cathode of tube 51. The voltage drop through resistor 59 is thus increased so as to reduce the bias applied through whereby carrier current of frequency FI is generated and transmitted through transformer 99 and coupler |I0, over the power line to each of the carrier subscriber stations. As the potential of the cathode of tube 51 rises, the voltage applied through condenser 56 and resistor 55 to gas-filled tube 53 is increased until discharge occurs in gas-filled tube 53. The potential of the starter anode of tube 51 is reduced due to discharge in tube 53. When the power voltage begins to fall, so also does the potential of the main anode of. tube 51; and, when this potential falls to a value which is insufficient to maintain a discharge between the main anode and cathode of tube 51, the discharge in tube 51 ceases, tube 53 isdeenergized and the potential applied to the grids of the transmitter tubes 8|) and 98 becomes suiiicientl-y negative to terminate the transmission of carrier current of frequency FI over the powerk line PL. The voltage between conductors 10 and 11, the capacity of condenser 56, and the resistance of element 55 are such that it takes 5a predetermined interval of time for the voltage Eacross the control gap of tube 51 to reachthe `time'for the voltage cross the control gap of tube 51 to reach the breakdownvalue. During the inu terval which is measuredby the charging of condenser 56, the winding 14 of power transformer PTI will have been energized by a half cycle of opposite polarity and by another half cycle of power wave of the polarity which tendsto` make the main anode of tube 51 positive with respect to ground; but no impulse of carrier current of frequency FI is transmitted during this period bevcause at the time the anode of tube 51 'becomes positive, the voltage across the control gap has not `reached a value sufficient to effect breakdown.

During the following half cycle of the power wave, while the mainanode of tube 51 is negative with respect to ground, the voltage across condenser '56increases' sufficiently to effect ionization-of the control gap; and as soon thereafter as the "voltage 'induced *in 'windingll once more *7 -inakesfth'e mainanodeof tube-51 sufficiently Vposi- .tivef-with`respect'to;ground,fthe main gap of :tube fflfis'ionized and'the'transmitter CTI is'lenergized to transmitanotherfimpulse of carrier-current-of frequency iFI. Thus every second .positive half #cycle of "theipower wave effects the/breakdown jef `-tube'Sf'I l.as long Vas relay 5I remains'operated. Thus, assuming Vtheipower. -line frequency toA be-60 `cyclesl per second, carrier current impulses of about??? .milliseconds duration are transmitted over the `:power 'line during 4each ringing inter- -val of theringingcode transmitted from connector 'Clover'lline '2I to relay 5I, the. impulses Abeing transmitted over the power line at a -rate of 30 impulses vpersecond.

If Bringing current. is received over the Aring conductor of .line .-2I :insteadoifthe tip conductor, vrelay 6l is operated-instead of relay 5I Vand-oscillat'or ORis energizedfin similar mannerto that in which :oscillator OT is 'energized as above described. The carrier ltransmitter` -CTI is thereby energized to .tranSmitcaIrier current impulses of 'frequency `1Ik over. power'linexPL at a rate 4of 30 iinpulsesper second 'during every second half cycle :ofthe voltage wave induced in `winding 1410i power transformer of the .polarity opposite to *that which effectsfthe-operation of oscillator OT. Thus 'when relay 5I `is operated, half'cycles vof one polarity of vthe power wave cause the operation of oscillator OT to send ringing signal impulses of `carrier lcurrent-over .power line PL; and when relay 6I iis operated,l fhalf cycles of the other .polarity ci :the .power wavecause'the operation 'oi oscillator OR to sendringin'g signal impulses of kcarrier current over the power line.

In some cases, the `central office maybe arranged -totransmit ringing current over one conductor'of a line "to ring the calling station lat the same time that ringing vcurrent is being transmitted 'over theother conductor of fthe-linetoring 'the 'calledstation. In such a'case, both of relays 5I Avand SI'. areoperated at the same time 'and car- .rier current 'is ktransmitted during both A the 4positive and negative halves of alternate :cyclesof fthe power voltage.

In case the-.connectors of the telephone central oilice are arranged. for 'bridged'code l'ringing `instead of divided `code ringing, both offrelays 5 I'and `I'l willfbe operated-:during 'leach ringinginterval, `In such acase, by strapping the outer front contacts ofrelays 5 Ifand' I together, .both relaxation oscillators will be actuatedevery second cycle 'of the power wave, one ioscilla'torduring the positive half cycle and the other oscillator during the Enegativelhalf cycle sothatthe carrier transmitter CTI will transmit impulses of carrier v`current of frequency FI over line PL to operate the ringers vat all of the carrier subscriber stations.

The 'ringingsignal impulses of carrier current of frequency FI generated byv `carrier transmitter CTLI responsive to ringing lcurrentincomingover line 2=I to carrier .terminal 'equipment CEI, :are transmitted` over .power line PL to feachof the lcarrier telephone subscriber stations. At each oilthese stations, the impulses of carrier lcurrent are `further transmitted through a coupler `yII=I, `conductors II2, through condens'ers-IZIS and IIB and transformer III'4 of filter unit FL2, and 'through transformer 'I I8 and resistors-I2! vand -1I22 of filter unit EL3 to the control 'zgrid of yamplifier. tubeI25. Theamplifi'ed ringing signal imfpulses of carrier -currentin `the output-circuit of tube L25 are transmitted through ltransformer '129 of lter unitFLAetothe-fgrid offamplifier tube i131 Although rtliefiilament cftube |32 fis nor-4 mallyfenergizedandgpositivefpotential supply confductor `I 93-is normallylconnected Fto the vplate of A.tube :I 32, fat feaoh` carrier subscriber station, the .tu-be IBZfat-each `vstationv Yis normally 4effective Lto amplifyathe ringing fsignal impulses either only during-half cycles of the power-Waveof .one polof'lthevoppositepolarity. This vvisdue. to the fact 'that the `potential -iof -the -screen grid .is .normally rcontrolled :by winding |85 -of tpower transformer -PT3, theffconnectionzbetween the grid of `tube 132 and thiswindingbeingtraced through resistors .'Ii-andzflf; amormallyclosedcontact of switch H4, randiconductor, -I 86. Therefore Aat each -of -halfof the carrierfsubscriber.stations, the windfing Milf-of transformer PTS makes fthe -screen igridfof the ampliertube 1.32 positive-during half cycles-of the g-powervwave-of one polarity; and, at each-of -the .other stations, -the Winding I 85 of the fpowerutransformer =P T3 makes the screen grid of the amplifier tube 1 I 32 .positiveduringhalf =cycles of thexpower-Waveof .the opposite polarity. The selective enabling of amplifier tube |32 during one phase or the other of the power wave can be :reversed if `ne'ce'ssar'yat anyrstation by interchanging the connection'sto the associated power supply v-transfomnepPT .Thusat each of some of. thestations, tube-T32 will be able to amplify vvringing .currentl .impulses received during one 1phase .of the. ,power wave; `and at each of the 'otherstationatuba|32 will be able to amplify ringingcurrentfimpulsesreceived during `the op- '.pulses .generated and. transmitted. responsive to the operation .of relay '5I of carrier terminal equipment vCEI- wil l..the'reafter 'be vreferred to as -the,tipstations andfthestations which are sig- .na'lle'd by. carrier-current impulses generated and transmitted-responsive to .the .operation of relay Ilofcarrier terminal vequipment CEI will be referredto as the ring'jstations. At each'o the stajtions -at which tube 'IiJZ is 'enabled Vduring the .half cycles ofthe power wave on 'which'the ring- ;ingsignal carrier current impulses are superim- .posed on annpltcular call, tube AT32 amplifies these impulses and -'the .amplified impulses are transmitted .through transformer M5 of lter unit rectifier T47, and' through thewinding of relay I 50. inparalle'l `with condenser I5 I, thence -to groundfat. the glower'most normally closed conf-tact of. switch. I'I. "Rela'y. -'I50'is a sensitive relay and isfaltern'a'telyoperated'and released responsive -to -ringing'sg'nal impulses received at the rate of thirty-impulsesper Asecond during each ringing `inter-vail.crit-he ringinglcode with'which the .called stationLs-.identied Each operation of relay I5Il closes circuits foroperatin'g relay I G0 and chargingcondenser |55. Thelcircuit for operating relay .'I' is ftracedffromground.through winding '4.85 (of Apower 'transformer PTB, conductor I86, ,rectiierfIS-Il, resistor lI`92,f-positive potential sup- ,.ply--conductor.[.93y resistor I 53, 'front contact of 'relay- I Sfresis'tor 151 winding-of relay |60, uppermost .back-contacter Yswitch 414, and resistor ,-If'I2 to ground. YThe .circuit vfor charging Vconresistor-,453,.front'contact of relay |50, condenser were |55, and through ringer |56 in parallel with resistor |59. Due to the shunt path throughresistor |59, the current through ringer |56 is insufcient to tap the bell responsive to the nrst operation of relay |50. The operation of relay |60 closes a short circuit across the resistor |12 and back contact of switch |14, and opens the shunt path through resistor |59 to render ringer |56 operative responsive to succeeding operations of relay |50 during receipt of ringing signal impulses. Relay |60 is a slow-to-release relay and remains operated while relay |50 is responding to ringing signal carrier current impulses at a rate of 30 impulses per second. When relay |50 releases at the end of the rst carrier current impulse, it closes a circuit through resistor |52 for discharging condenser |55. Each succeeding operation and release of relay |50 responsive to ringing signal carrier current impulses charges and discharges condenser |55 in series with ringer |56; and the ringer at each of the tip carrier subscriber stations is thus actuated in accordance with the ringing code of the called station. On a call on which ringing' current is transmitted over the ring conductor of line 2|, the ringer at each of the ring carrier subscriber stations is actuated in accordance with the ringing code of the called station.

When the receiver is removed from the hook at the called carrier telephone station, ground is connected through resistor |12 to reduce the bias of the vacuum tube of the carrier transmitter GT3, the short circuit across receiverL |16 is opened, and the screen grid of tube |32is transferred from the winding |85 to the plate supply conductor |93 so that tube |32 is no longer disabled during alternate hal-f cycles of the power wave. The actuation of switch |14 upon removal of the receiver is also effective to close a circuit (not shown) for energizing the lament of the amplier tube (not shown) of the carrier transmitter GT3. If the receiver is removed during a silent interval of the ringing code, relays |50 and |60 will not be operated, and with relay |60 normal crystal |62 is included in the frequency determining circuit of the oscillator of carrier transmitter GT3 and carrier circuit of frequency F2 is generated and transmitted through filter |65 over the power line PL. yIf, however, the receiver is removed while relays |50 and |60 are operated responsive to ringing signal impulses, crystal |63 is included in the frequency determining circuit of the oscillator of carrier transmitter GT3; but relays |50 and |60 release during the next silent interval of the ringing cycle and crystal |62 is thereupon connected in the frequency determining circuit 4of carrier transmitter GT3 to effect the transmission of carrier current of frequency F2.

The carrier current of frequency F2 transmitted from the answering carrier subscriber station over line PL does not aiect the carrier receivers at the other carrier subscriber stations, since lter units FL2 and FL3 are tunedtopass a carrier band including frequency FI but excluding frequencies F2 and F3.. Since .the receiving lter of carrier receiver GRI at the carrier terminal CEI is tuned to pass a band including frequency F2, the carrier current of this frequency transmitted from the answering carrier station passes through coupler ||0 andreceiving lter |0| of carrier. receiverGRl of the carrier terminal equipment CEI, to the` input circuit of amplier |02. Rectier element |06 vtransmits a part ofv the output of ampliiier: 102V to effect the energization of the windings of relays 41 and 4| in series; and rectifier element |05 transmits voice frequency components'f'in the output circuit of amplifier |02 through con"- denser 49 and windings 3| of hybrid coil HC. The operation of relays 41 and 4| by the rectied carrier current of frequency F2 is delayed for a predetermined, interval of time', while condenser 43 ,is charging to prevent operationoi the relays by static or otherA momentary 'disturbances on line PL. The operation of'relay 4| opens a normally closed short circuit across relay 4.5 and closes a circuit aforoperating relay 42. The operation of relay 42 connects theconductors of line 2| to windings 30 of hybrid coil HG; and with relay 41 also operated these wind'- ings are connected in series across the conductors of line 2| tov cause the operation of the `ringing trip relay (notshown) of the connector C| and the closing of the talking path through the connector between the calling station I0 and line 2|. The aforementionedoperation of relay `'42 closes a short circuit across resistor 89 to reduce the grid vbias of tube andclosesa short'circuit across resistors 38 and 36 to reduce the grid fbias of tube 98 -so that `carrier current of frequency Fl istransmitted through transformerllljand couplerv ||0 over power line PL. Voice currents incoming over line 2| from the calling station |0 are impressed through windings 30 and 32 of hybrid coil HG on a grid of tube .80 thereby= to modulatethe carrier current of frequency Fl being .transmitted over the power line. *Thus two-way transmission between station |0 and the called carrier station is elected andthe connection is maintained until released at the'callf ing and called stations. When the handset is replaced on the hook at the called carrier sub#- scriber station, the switch |14 is restoredvto normal thereby deenergizing carrier Atransmitter GT3; but relays |50 and ,|60 remain operated at each of the carrier stations until carrier transmitter GTI of the carrierY terminal equipment is also deenergized. When the transmission of carrier current', of frequency F2 vfrom carrier transmitter GT3 ceases, relays,41v and 4| ofthe carrier terminal equipment GEI releases. lThe release of relay 41 opens the bridge across the conductors of line 2| and the release of Arelay 4| causes the release of relay 42. The release of relay 42 reconnects line 2| to ringing relays 5| and 6|, opens the short circuit across biasing resisto-r 89 and opens the short circuit across .biasingresistors 38 and 36 whereby the transmission of carrier current of frequency Fl `from transmitter -C'II `is ended and relays |50l and |60 at. each of the carrier -subscriber stationsy arie released. -The line-iinderLFl and selector Sl arefrestoredgto normal inusual and well-known lmanner when the receiver is replaced at the calling station |0. A

Gall from ,carrier subscriber. station to station I10 Assume now lthat the handset |15 is removed from the receiver hook .at one4 of the carrier subscriber stations to initiate acallto station 0.

lWhen switch |14 vis actuated'by removal ofthe givers CRS'YMB tuned t0. ,Pesse ,tendre-:Itegem asi-c2763 1T notfincludefrequency F2.. Atlv the carrier termi'- nal equipment CEI, the. carrier. currentv offrequency- F2Vv passes.v through |01" of` carrier receiver CRL and., effect'sthe. operation of'. relays 41 and 4|.. The operationof relay 4| causes the loperation.of'relay. 42;.and, with both oi relays 41 and-r 42 operated the windingsA 3D.' of hybrid coil.- I-IC` are connectedli'n series with the corrductors of'line..2|. to=cause theoperation ofthe linerelay-(notshowni of line circuit 22,Y anda line-finder Lli2fv isthereupOrly operated to extend thecallingrlinelfl to, a..first` selector S22 The aforementioned.. operation of'. relay 42 also relducedY the lbiasfof tubes. andllinthe' manner hereinbefore describedto cause carrier transmitter` CTI4 to transmit. carrier current of fre'- quency .FI- over. -power line PL. 'This carrier current4 isamodulated by dial tone transmitted from/selector. S2 throughV line-finder LF2`, line 2|! and.` windings. 30`r and 32 of' hybrid` coil. HC to the inputcrcuit oft'ube- 801 When the calling-A subscriber. hears the dial tone. the directory number. of the. called station |0` is dialed. The circuitthroughreceiver |16 is opened .attlie orfnormal contacts .of dial and the` impulse contacts of'the dial open and" close the connection between.` plate supply conductor |93" and ampliflerfmodulator |64 of carrier transmitter .C1-*3T to transmit a train of dial impulses correspondingT to each digit! dialed, `each dialL impulse being transmittedas an' interruption vof the carriercurrent of frequency F2'. With relay 42 of carrier terminal equipment CT` operated, condenser 43 is connected in parallelwith the Windi'ng.v of4 relay 4|` alo'n'egso that' relay 4T becomes fastA in operating and releasingandrelay" becomes slow in releasing; sothatrelayhremains operated' during the; receipt of" dialE impulses: but rel'ay 41V isA released and.- reoperated' responsive to eacl impulse.: Each release Vofirelay 41 opens-the bridge across' the conductors of lineV 21. The first trainy of' dial impulses is' thusk repeated over line 2|" tot effect the'selectiveoperation of selector S2.

The` connection is extended by the' operation of selectorS2` to an idle' conductor C2" having? access tothe called line. The'remainingj' digits dia-led bythel calling subscriber' effect the selective op'- erationof connector-C2" toconnectl withthe` called lne^| |`L and toselect the ringingcode witl'i'which A, station lis signaled; The connector C2' makes theusuallbusy test andI if'line` I1' is idle', the selected" ringing' code" is transmitted over line |'I to signal the called'subscriber. When the called subscriber answers, the ringing trip relay (not Yshown)4 of connector4 C2" isI operated' -toterminate the ringing :md Vthe talking connection is estab'- lishjed' betweendliies 2|fand"|-"|. Voice currents from transmitter |11 of handset |15 modulate the carrier current of frequency 'F2 transmitted over th'epmiver line Pl'ifrom' the' calling station;

and the carrier receiver CRI transmitsthese-voice currents through demodulator |05, condenser 49, windingsl and 30 ofhybridcoilHQ over line- 2| .through line-finderl LF2 selector S2, connector set |15 isreplaced on the receiver hookv at the calling station, at which time, the carrier transmitterCT isdeenergized causing the release of relays 41', 4| and 42 of carrier terminal equipment CEL The release of relay 41 opens the bridge across the conductors of line 2| whereby the connector C2, selector S2 and line-finder LFZ are restored to normal in usual and well-known manner. The release of relay 42 deenergizes the carrier transmitter CTI to stopthe transmission of carrier current of frequency FI over line PL and relays |50 and |60 are thereby released at each of the carrier subscriber stations.

Revertzng call A call from one Yof the carrier subscriber stations to another of these stations on the same line. and using the same carrier frequencies is known as a reverting call. Such a call is initiated inf the same'manner as any other call andthe removal of the handset and operation of thedial at. the calling station eiect the operation of a liner-lnder.l LF2, selector S2 and connector C2 to connect with the. called. line. The connector C2y is arranged to make a reverting call test in case the called line is found lbusy when connection is made therewith. A connector arranged to makea reverting; call.- test is disclosed in the patent. .to H. Hovland; No; 1,849,087-, granted Marchr1'5. 1932. Busyy tone is transmittedfrom theconnector C2: tothef calling station and the subscriber thereat thus restores the handset to normal to: permit ringing of. the called. station. When'- the handset is-.restored to normal at the calling station; carrier transmitter GT3 is deenergized and they transmission of carrier current. of-frequencyF2 over line PL is terminated thereby causing the-release of relays 41, 4| and 421. ofi carrier terminalvCEl. Thefbridgeacross the'conduct'orsloff vline 2| is opened7 by the release Yof relay-'41e andl the connector C2 then makes the revertive busy test above mentioned. Since the .call being, described is a reverting call, the Vconnector nds that the called line 2| is also thel calling line and the -line-nder. LEZ and selector S2 are thereupon- .restored to normal. The'connector C2is-held however withits brushes in engagement with. theterminalstowhich line 2|" is connected andringingY current is. transmitted` according. tothe selected ringing. code over either the tipor the ring conductor of line,2l| depending ori-.whether the called station is a tip` station or a ring. station. The one or the other of ringing relays. 5|. and 6| is operated by the ringing current to effect the transmission ofimpulses of carrier current` of frequency FI from carrier transmitter CTI. over ther power line PL to actuate the ringersat allof the tip stations if the. calledstationv is a tip station or to actuate. theringers at all of the ring stations if the. called stationis. aringr station. If the calling station is. not signaled" on. the same side of the line 2| as is the called station, a short impulse of.L ringing current is' transmitted" at the end of each. ringing. code cycle to eiect a short operation. of the ringer at the calling station so that. the calling party |will know, when ringing ceases, that the call. has .been answered.

When the vhandset is removed from the receiver hook at the called station to answer the call, carrier transmitter CTS will be energized to transmit carrier current of frequency F2 over the power line PL, thereby operating relays`4l and` 4110i the carrier terminal equipment CEI. Relay'll ll operates relay 42 and with relays-'415 and 13 42 both operated windingsf30 of hybrid coil HC are bridged across the conductors of line 2| to effect the operation of the ringing triprelay (not shown) of' connector C2. The transmission of ringing currentl is' thereby stopped and the brushes of connector C2 remain' in engagement with the terminals of line 2| as long as the bridge is maintained across the conductors of line 2|. With relay 42 operated, carriertrans-- mitter CTI is energized to transmit carrier current of frequency Fl, thereby operating relays |50 and |60 at each of thecarrier subscriber stations. When the subscriber at the calling station realizes the ringer `is no longer being actuated, the handset is removed for conversation with the subscriber at the called station. Although the operating circuit of relay |60 is opened when the switch |14 is actuated by removal of the receiver at the 'callingstatiom relay I6 isl held operated independent of the switch |14 as long as relay |50 remains operated. With relay I 60 operated crystal |63 is included in the frequency determining circuitv of the oscillator tube of transmitter GT3, and energization of the carrier transmitter by the actuation of switch |14 causes the transmission of carrier current of frequency F3 overthe power line PL. The carrier current of frequency F3 thus transmitted over line PL is :without effect at any of the carri-er subscriber stations but at the carrier terminal CEI', this current passes through lter'llll of carrier receiver CR 2 to amplifier |08. The current in the output circuit of amplifier |08 is demodulated by rectifier |09; and since the short circuit across the winding of relay 45 has been opened by the operation of relay 4| responsive to carrier current of frequency F2 received over'line PL from the called carrier subscriber station, relay 45 is operatively energized.

Relay 45 closes a circuit for operating relay 44.

The operation of relay 44`opens the operating circuit of relay 45 and connects the output of demodulator I 09 to windings `3| of hybrid coil HC. Conversation between the calling and called stations is thus enabled, voice currents from the telephone transmitter' |11 at the called station being effective to modulate the carrier current of frequency F2 transmitted from lthe `associated carrier transmitter GT3 over line PL to carrier receiver CRI of the carrier terminal CEI. The voice current components ofthe carrier current of frequency F2'received from the called station are transmitted through demodulator |05, condenser 49 and windings 3| and 32 of hybrid coil HC to modulate the carrier current of frequency FI transmitted from carrier 'transmitter CTI overline PL vto; both the' calling and called carrier subscriber stations. The voice currents from the telephonetransmitter |11 at the calling station modulate thel carrier current ofv late the carrier current of -frequency FI- transmitted from carrier transmitter CTI over line PL to both the calling and called carrier'subscriber stations. e Y

If the calling subscriber restores the handset to normal at the same time orbefore the handset is restored at the called station; the associated carrier transmitter'is deen'ergized to terminate the'vtransmission ofcarrier 'current of frequency F3, relay of carrier terminal CT being thereby released. When the carrier transmitter yat the called station is alsodeenergized, the'transmission of carrier current of frequency F2 is terminated thereby causing the release of relays '41, 4I and 42 of carrier'terminal CEI. The release of relay 42 deenergizes carrier transmitter CTI thereby causing the release of relays and |60 at each of thecarrier subscriber stations. The release of relay 41 opens the bridge across line 2| thereby causing the connector C2 to be restored to normal in usual man#- ner.

If therhandset is restored to normal at the called station before the connection is released at the calling station, the deenergization of the carrier transmitter at the called station causes the release of relays 41 and 4| of carrier terminal CEI. The release of relay l41 opens the bridge across the conductors of line 2| and the release of relay 4I causes the release of relay 42. The release ofv relay 42 restores the normal grid bias of the carrier transmitter tubeA to terminate the transmission of carrier current of frequency FI over line PL and thereby release relays |50 and I60`at each of the'` carrier subscriber stations. The release of relay at the calling station at which the receiver has not yet been replaced on the receiver hook, changes the tuning of carrier transmitter CT3 by inserting crystal |62 in place of crystal |63 in the frequency determining circuit of the oscillator so that the carrier current transmitted therefrom 'is changed from frequency F3 to frequency F2. This change in thefrequency of the carrier circuit transmitted over line PL from the calling station causes the release of relays 45 and 44 and 4the reoperation of relays 41, 4| and 42 of carrier terminal CEI. The reoperation of relays 41v and 42 again closes the bridge across the conductors of line 2|. If the interval during which relays 41 and 42 were released is suiiciently long the connector switch C2 is at the time restored to normal; and in such a case the reclosing of "the bridge effects the operation of the line relay of line 2| and the starting of a line nder. The reoperation of relay 42 again energizes carrier transmitter CTI so that carrier current of frequency Fl is again transmitted over line PL, operating relays`|50 and |60 at all carrier subscriber stations except the calling station at which relay |50 is operated but the circuit for operating relay |610 is open at a contact of switch |14. When the handset is replaced 'at the callying station the carrier transmitter GT3 is deenergized causing the release of relays 41, 4I and .42 at the carrier terminal CEI. The release of Irelay 41 again opens the bridge across the conductors of line 2| thereby to effect the return of connector C2 to normal, if not already returned to normal; or if connector C2 was returned to normal before the carrier transmitter -at .the calling station started to transmit carrier current of frequency F2, the opening of the ,bridge across the conductors of line 2| causes the release 'of the line-finder which wasoperated to connect the line 2| after'v therconnector'CZ was released.

The carrier transmitter CE2 shown in Fig. 5 is `similar to carrier terminal CEI shown vin Fig. 2

`except that it is arranged to receive four-party loop across the tclephoneline 2 I... transients. might. varyi thepotential oi the; grid of tube, 8u suiiicientlytoV cause bell tapping .at.. the

beenf modifiedas hereinafter describedy Riefenenoeimayrbe hadi to, the patent, to, BI". Honland; 1;849\,QB8-, -gnantedMarch! 1'5, 19.32', for disclosure offesconnectorfarrangedifor four and-eight-.party superimposed ringing; Four ningingrelaysV are providedl in; carrier terminal CEniiela/sl 5ML and Sliffor, responseI to: ringing current received over the-tip conductor-ethno V2l and relays. EIL and Bil-2 for r-esponseto ringing currentreceived over thc-ring conductor offline- ZI. The 'windings of cachot the ringing.- relaysisv connected to the;- line conductors through aA two-element gas-lledtube; relayssEII andilil being thereby polariaedto respond to iringing,r current and relays SI2 and 64.2 tmrespondy to.- i-if` ringing current. Four relaxation oscillator-SQTIWOTZ, ORI. and OR?, are providedr one for each of relays 5,1 I.&I-2,.SI. I. and 6ft-2 OscillatorsQTi and ORI- areident-icalf/with oscillators. @Tand @R et the carrier. terminal GEI shown in-Fig.., 2; and oscillators 0T2 and @B2i-are similar exceptthat, in cach of. these.` the vaiuesof the-.capacityv-and, resistances which con.- trolthetimerequiredi for'impressing the breakdown, voltage across. the; control` gap of.. the threeclement. gas-filled, tubes- 551. andv: aresuch. that the main gap; off tube G51., becomes ionized` every tbirdlpositivenal cycleofthe'powier voltage and the main'i gap of' tube` 65,1.. becomes ionized. every third negativa half cycle of the power voltage. Thus, assuming'thepower supply frequency to be @Bicycles per second, the carrier-.transmitter CTI ist energized to transmit ringing signal carrier current; impulses at the. rate. of 30. impulses per second when ringing relay. 5H. or 6H andthe associated oscillatorv OTI. or. OR I: are energized; and tot transmit ring-ing signal! carrier current. impulses at the rate or 20..impulses per-secondi when ringing. relay 512` or 6 I2. and the. associated oscilllater-@T2012 @R2 lare energized.,

Inorder tofinsure against bell-'.tappingat carrier subscriber stations due to modulation ot the carrien transmitted from. carrier transmitter. CTI duringgthe repeating of. dial impulsesfiromaoalling carrier station to the central` oiiicavthe arrangementoi relays 4I ,42 and 4J. differs iromthat shown inrliig. 2; Relay 41, alone is, energized in serieswith rectifier LGB responsiveto carrier current incoming to, receiver CRI from the calling carrier sta.- tion. yRelay-1i?! controls both. relay fil. and; relay 42, relay 4+ being. fastto follow dial impulses and relay 42-A beingf slow to: release so as.toremain.Opn cratedduring. dialing. The operation of relay. 4 2 connects the gridv oftube 8B to the back. Contact o-,1'.elay-.4I.-. -Each release of: relay, .47, groundsthe grid ot tubefto maintain the, output of tubes dit andi-98' substantially constant. at a time when transients mayA be. created by the. opening ofthe Otherwise such carrier subscriber stations, otherl thang the calling station. However,. by grounding thegrid of .tube

v813- when relayf 41 releases, the carrier current. being; transmitted trom transmitter GTI. remains substantially constant during dialing. Tliewind- .ings of: the hybridl coil Vare so connected and the central cnice catteryis sovpoled thatA the grid. of

.tuberSxIlA maybecome morepositive 'when the loop over the telephone line is closed at the endiof each dial impulse, but the increaseof carrier current tive superimposed. ringing arel schematically rep- "resented-1 by the.` station s hown-n Fig. 3. The dit- 16 ference; between, stationszar-ranged for divided coderingingjand stations arrangedifor four-party selective andv eight-party:semi-selective ringing.v is thatther-ingers at stations arrangedfor-.four and eight-party ringing A are tuned tol respond either tocarrier` impulsesincoming at. the rateo f impulses-..per second or to carrier impulsesiincom.- ingrat. the-rate of: 20.-impulsesper second. When therearef only tous, stationseach station Vis signaled. by alone-ring; code; andwhen thereare eight. stations,A thefiour additional: sta-tions are signaled-by ai two-ring-code. Fig. 6. shows the various ringing conditions established; by theconnectorsfin thev central oilice forfour and. eightparty ringinganct shows theringing relays and oscillatorsot thefcarrier terminalgwhich are energized and the ireqnencyvof thsringing signalicarrier current impulses vfor ringing eachi station.

Whatiseclaimedf l. In a telephone system, subscriber lines in;- cluding; party linesha plurality ot subscriber stations connected to-eaoh Qfrsaid party. lines, me ans for connecting`1 calling, and called. lines, means for transmitting ringing current over one conductor oi acalled.party-'lineftoringfcertainiof the stations onthe lino; andfor transi'nittingt ringing. current over-the other conductorto-fringt the other stationsonV theline,` afpower lima. a plurality. of telephone stations connected to said power line, each ot said'` powen. line stationsy arranged` for`v carrier current operation-oven said power line-carrier terminal'. equiprn eI-rt;.connectingl sadpower line to one or said party lines; and: means. including means.: in said carrier-terminal: equipment and means ateach of: said power linev stations for ringing certain. off saidxpowerline stations when ringing currenti's receiyedvaby said carrier terminal equipment overone; conductor Vof'.- said onev party line and' for rirvging| the other; power; line.: stations Wirren.` ringing current,` is.; received; bysaidi. carrie-r terminali equipment overtlie. other conductor`A 0f said. one-.party line,A

2. I nf a signalingfsystem, a4 carrier; current transmitter a plurality off carrier; current; receiv.- ers;` cache including;l signal; means;4 a1 transmission medium .com-mon, to said transmitter and' receivers for: transmitting` carrier; current.- from said trans;- mitten to allfofsaid. receivers, means fon impressing an alternating current oontrolfvoltage on ksaid medium, azirstlcontrol means for rendering said transmitter` eiectiveto transmit. carrier current of a particular frequency over said. medium-- a second controlfmeansv for rendering said transmittereffective totransmit carrier currentv orsaid particular frequency over said medium, means fory selectively rendering; either saidfirsty control meansrorsaidi second-control means eiective to control; saidi transmitter, athird control means, in each of sement; said-freceiversL for rendering the receiverI effective-to. actuatc-r the associated sig-nal meansresponsive-to oarriertcurrentof said particular frequency transmitted over said-medium, a.` fourth control.r meansin. each of the remainder of. said receivers for rendering. the receiver effective togactuatetheassocated signal means responsivefto. carrier-current of .saidparticular frequency transmitted overl saidv medium, means responsive to. alternatahali cycles, oi one polarity ot said control voltage. 'for rendering saidrst and third control-1 means effective, andv means. responsive to alternate half cycles of the opposite. polarity of, saidcontroi voltage for rendering. said secondi and fourth, control means; eective.

3,.. InY a. signaling` system. a, carrier current transmitter-,arranged to. transmit, carrier Current 17 of a particular frequency, .a plurality of carrier current receivers each including individual signal means, a transmission medium common .to said transmitter and receivers for transmittingcarrier current from said transmitter to .all of `said receivers, means for impressing an alternating current control voltage onsaid medium, a iirst con-- trol means for rendering said transmitter effective to transmit carrier current over said medium, a second control means for rendering said transmitter effective to transmit carrier current over said medium, a third control means for rendering said transmitter effective to transmit carrier current over said medium, a -fourth control means in each of some of said carrier receivers for rendering the receiver effective to actuate the associated signal means responsive to carrier current of said particular frequency incoming over said medium, a fifth control means in each of the remainder of said carrier receivers for rendering the'receiver effective to 'actuate the associated signal means responsive to carrier current of said particular frequency incoming over said medium, means responsive to half cycles of one polarity 'of said control voltage for rendering said first and fourth control means operative, means responsive to half cycles -of the opposite polarity for rendering said-second and fifth control means effective, and means for-operating said third control means independent of the polarity lof said control voltage.

4. In a signaling system, a carrier current transmitter comprising an amplifierand arranged to transmit carrier current of a particular frequency, a plurality -of carrier current receivers each comprising an amplifier and a signal device for yoperation responsive to carrier current of said particular frequency incoming to the receiver, a transmission medium common to said `transmitter and vreceivers for transmitting carrier current from said transmitter to all of said receivers, means for impressing analternating current control voltage on said medium, means normally biasing the amplifier of said carrier transmitter to prevent the transmission of carrier current over said medium, a first control means opera ltively responsive to alternate half cycles of one polarity of said control voltage for rendering said amplifier effective to transmit carrier current, a second control means operatively responsive to alternate half cycles of the opposite polarity of ksaid control voltage for rendering said amplifier effective to transmit carrier current, means for selectively placing the one or the other .of said ycontrol means in control of said transmitter,

means in each of some of said receivers for rendering the amplifier therein effective responsive to half cycles of said one polarity of sa-id control voltage to amplify carrier current of said particular frequency incoming over said medium thereby to operate the associated signal device, and means in each of the remainder of said receivers for rendering `the amplifier therein effective responsive to half cycles of said opposite polarity of said control voltage to amplify carrier. current of said particular frequency incoming over said medium thereby to operate the associated signal device.

5. In a telephone system, a voice frequency telephone line comprising two conductors, a power transmission line, a plurality .of telephone .subscriber stations connected to said power line, carrier terminal equipment individual to said lines comprising a carrier current transmitter for transmitting carrier current over said power line,

18 `means for selectively impressing a desired one of a plurality of ringing codes on the one or the other of said conductors to .signal a called one of said stations, a first ringing relay connected to one 'of said conductors for response to ringing codes transmitted thereover, a second ringing relay connected to the other of said conductors for response to ringing codes transmitted thereover, a iirstk relaxation oscillator comprising a three element gas-lled tube operative while said first ringing relay is operated, a second relaxation oscillator comprising .a three element gas-filled tube operative while said second ringing relay ,is operated, an oscillator in said carrier transmitter rendered operative while either one of said ringing relays is operated, a vacuum tube amplifier in said carrier transmitter normally biased to prevent .the transmission of. carrier current from said oscillator `over said ,power line, means including a transformer winding energized by said power line `and timing means associated with the gas-filled tube of rsaid iirst oscillator for effecting discharge .of the gas-filled tube during, alternate half cycles of one polarity of the power line voltage, vmeans including a transformer winding ener gized by said power line and timing means associated with the ,gas-filled tube of said second oscillator for effecting discharge of .the gas-filled tube during alternate half cycles of the opposite ,polarity of thepower `line voltage, means for decreasing the bias of said amplifier when either of said gas-filled tubes is energized thereby to render said amplier effective .to transmit carrier current over said power line, each of said subscriber telephone stations comprising carrier current receiving means including a vacuum tube amplifier and a detector and a signal device energized by carrier current incoming over said power .line from. said carrier transmitter, `means ,at each of some of said subscriber stations comprising a transformer winding energized ,by the power line for rendering the amplier of the carrier receiver operatively responsive to carrier current superimposed on half cycles of thepowcr line voltage of said one polarity, means at each of the others of said subscriber stations comprising a transformer winding energized Aby the power line for rendering the amplifier of 4the carrier receiver .operatively responsive to carrier current superimposed on half cycles .of the power line voltage y.ofsaid opposite polarity, and signal means at each ofsaid .carrier stations energized by the energiza- .tion of the signal device responsive to impulses of carrier current received over said power line while the amplierthereat is operative.

6. 'In a signaling system, a carrier current transmitter, a plurality .of carrier current receivers, each Yof said receivers including individual signal means, a powerline icommon to said trans-. ,mitter and receivers, means for controlling ,said .carrier transmitter to transmit carrier current through said 4power line tol all of said receivers only .during half cycles of one polarity of the power line voltage, means for controlling said carrier transmitter to transmitl carrier current Athrough said power line to all 'of said receivers only duringl'ialf cycles of the opposite` polarity of .said power line voltage, means for controlling said carrier transmitter to transmit carrier current through said power 'line to all of said receivers during ,half cycles of both polarities of the power line voltage, means in each .of some but not all of said receivers for Yactuating ,the associated signalmeans responsive only to carrier current received throughv said medium during 19 half cycles of said one polarity of the power line voltage, and means in each of the remainder of said receivers for actuating the associated signal means responsive only to carrier current received through said medium during half cycles of said ,opposite polarity of the power line voltage.

`medium, means for selectively rendering either said Iirst control means or said second control means, or both said rst and second control means at one time, eiective to control said transmitter, a third control means in each of some of said receivers for rendering the receiver eifective to actuate the associated signal means responsive to carrier current transmitted over said medium, a fourth control means in each of the remainder of said receivers for rendering the receiver eective to actuate the associated signal means responsive to carrier current transmitted over said medium, means responsive to alternate half cycles of one polarity of said control voltageifor renderingsaid iirst and third control means eiective, and means responsive to alternate half cycles of the opposite polarity of said control voltage for rendering said second and fourth Icontrol means effective.

, 8. In a signaling system, 'a 'carrier current transmitter comprising an amplifier, a pluralityI of carrier current receivers each comprising an amplifier and a signal device for operation responsive to carrier current incoming to the receiver, al transmission medium common to said transmitter and receivers for transmitting carrier current from said transmitter to all of said receivers, means for impressing an alternating current control voltage on said medium, means normally biasing the amplifier of said carrier transmitter to vprevent the transmission of carrier current over said medium, a rst control means operatively responsive to alternate half cycles of one polarityv of said control voltage for rendering said ampiliiier effective to transmit carrier current, a second control means operatively responsive to alternate half cycles of the opposite polarity of said control voltage for rendering said ampliiier effective to transmit carrier current, means for selectively placing the one or the other or both of said control means in control of said transmitter, means in each of some of said receivers for rendering the amplier therein effective responsive to half cycles of said one polarity of said control voltage to amplify lcarrier current incoming over said medium thereby to operate the associated signal device, and means in each of the remainder of said receivers for rendering the amplifier therein effective responsive to half cycles "of said opposite polarity of said control voltage to amplify4 carrier current incoming over power transmission line, a plurality of telephone carrier terminal equipment individual to said lines comprising a carrier current transmitter for transmitting carrier current over said power line, means for selectively impressing a desired one of a plurality of ringing codes on the one or the other of said conductors to signal a called one yor said stations, a rst ringing relay conriected to one of said conductors for response to ringing codes transmitted thereover, a second ringing relay connected to the other of said conductors for response to ringing codes trans mitted thereover, a rst relaxation oscillator comprising a three element gas-iilled tube operative while said rst ringing relay is operated, a second relaxation oscillator comprising a three element gas-nlled tube operative while said second ringing relay is operated, an oscillator in said carrier transmitter rendered operative while either one or both of said ringing relays is operated, a vacuum tube ampliiier in said carrier transmitter normally biased to prevent the transmission of carrier current from said oscillator over said power line, means including s. transformer winding energized by said power line and timing means'associated with the gasiilled tube of said rst oscillator for effecting discharge of the gas-lilled tube during alternate half cycles of one polarity of the power line voltage, means including a transformer winding energized by said power line and timing means associated with the gas-filled tube of said second oscillator for effecting discharge of the gas-filled tube during alternate half cycles of the opposite polarity of the power line voltage, means for decreasing the bias of said amplifier when either or both of said gas-filled tubes is energized thereby to render said amplier effective to transmit carrier current over said power line, each of said subscriber telephone stations comprising carrier current receiving means including a vacuum tube amplier and a detector and a signal device energized by carrier current incoming over said power line from said carrier transmitter, means at each of some of said subscriber stations'comprising a transformer winding energized by the power line for rendering the ampliiier of the carrier receiver operatively responsive to carrier current superimposed on half cycles of the power line voltage 'ci said `one polarity, means at each of the others of said subscriber stations comprising a transformer winding energized by the power line for rendering the amplier of the carrier receiver operatively responsive to carrier current superimposed on half cycles of the power line voltage of said opposite polarity, and signal means at each of said carrier stations energized by the energization of the signal device responsive to impulses of carrier current received over said power line while the ampliier thereat is operative.

10. VIn a signaling system, a carrier current transmitter, a plurality of carrier current receivers, individual signal means controlled by each of said receivers, a transmission medium common to said transmitter and receivers for transmitting carrier current from said transmitter to all of said receivers, means for impressing an alternating current control voltage on Asaid medium, means for controlling said carrier transmitter to transmit impulses of carrier current over said medium only during half cycles of one polarity of said control voltage, the frequency oi said impulses being an integral subatraves multiple 'of the frequency of said controlvoltage,

and means in 'each of some but not all of said vreceivers `for actuating the associated Vsignal means responsive only to carrier current received through said medium during half -cycles of said 'f' one polarity of saidcontrol voltage.

11. In a signaling system. a carrier current transmitter, a plurality` of carrier current receivers, individual signal means controlled by each of said receivers, a transmission medium common to said transmitter and receivers for transmitting carrier current from said transmitter to all of said receivers, means for impressing an alternating current control voltage on said medium, means forcontrolling said carrier transmitter to transmit impulses of carrier current over said medium only-during half *cycles of one polarity of said'control voltage and at an impulse frequency which is an integral submultiple of the frequency of said control voltage,

.means for controlling said carrier transmitterto 'transmit impulses of carrier current over said 4medium only during 'half cycles `of the opposite .polarity of said control voltage and atisaid Timpulsefrequency, means in each of some `but not .all of said receivers for actuating the associated signal .means responsive only to carrier current received through said medium during half cycles of said one polarity of the control voltage, and means in each of the remainder of said receivers for actuating the associated signal means responsive only to carrier current received through said medium during half cycles of said opposite polarity of the control voltage.

12. In a signaling system, a, carrier current transmitter, a plurality of carrier current receivers, a transmission medium common to said transmitter and receivers for transmitting carrier current from said transmitter to all of said receivers, means for impressing an alternating current control voltage on said medium, means for controlling said carrier transmitter to transmit impulses of carrier current over said medium at a iirst impulse frequency which is an integral submultiple of the frequency of said control voltage and only during half cycles of one polarity of said control voltage, and means for controlling said carrier transmitter to transmit impulses of carrier current over said medium at another impulse frequency which is an integral submultiple of the frequency of said control voltage and only during half cycles of said one polarity of said control voltage.

13. In a signaling system, a carrier current transmitter, a plurality of carrier current receivers, a transmission medium common to said transmitter and receivers for transmitting carrier current from said transmitter to all of said receivers, means for impressing an alternating current control voltage on said medium, means for controlling said carrier transmitter to transmit impulses of carrier current over said medium at a first impulse frequency which is an integral submultiple of the frequency of said control voltage and only during half cycles of one polarity of said control voltage, means for controlling said carrier transmitter to transmit impulses of carrier current over said medium at said first impulse frequency and only during half cycles of the opposite polarity of said control voltage, means for controlling said carrier transmitter to transmit impulses of carrier current over said medium at another impulse frequency which is an integral submultiple of the frequency of said control voltage and only during half cyfao ing half cycles of'said opposite polarity of said control voltage'.

14. In :a signaling system, a carrier current transmitter, va plurality of carrier current receivers, a transmission medium common to said transmitter and' receivers for transmitting carrier current'from said transmitter to all of said receivers, `means 'for impressing yan alternating current control voltage on said medium, means for controlling said carrier transmitter to transmit impulses of carrier current over said me.-

,dium' at 'a rst impulse frequency which is an integralsubmultiple of the frequency of said conytrol voltage and only during half cycles of one polarity of said control voltage, means for controlling said carrier transmitter to transmit impulses of carrier current over said medium at an- .other' impulse .frequency which is an integral `submultiple o'f 4the frequency of said control voltage and only during half cycles of said one polarity of said Vcontrol voltage, individual signal means .including a tuned ringer controlled by each of said receivers, and means in each of said receivers for actuating the associated signal means responsive only to carrier current received through said medium during half cycles of said one polarity of said control voltage, the ringer associated with each of some but not all of said receivers being tuned to respond only to carrier impulses received over said medium at said first impulse frequency and the ringer associated with each of the other receivers being tuned to respond only to carrier impulses received over said medium at said other impulse frequency.

15. In a signaling system, a carrier current transmitter, a plurality of carrier current receivers, a transmission medium common to said transmitter and receivers for transmitting carrier current from said transmitter to all of said receivers, means for impressing an alternating current control voltage on said medium, means for controlling said carrier transmitter to transmit impulses of carrier current over said medium at a iirst impulse frequency which is an integral submultiple of the frequency of said control Voltage and only during half cycles of one polarity of said control voltage, means for controlling said carrier transmitter to transmit impulses of carrier current over said medium at said first impulse frequency and only during half cycles of the opposite polarity of said control voltage, means for controlling said carrier transmitter to transmit impulses of carrier current over said medium at another impulse frequency which is an integral submultiple of the frequency of said control voltage and only during half cycles of said one polarity of said control voltage, means for controlling said carrier transmitter to transmit impulses of carrier current over said medium at said other impulse frequency and only during half cycles of said opposite polarity of said control voltage, individual signal means including a tuned ringer controlled by each of said receivers, said receivers divided into four groups, means in each of the receivers of the rst and second of said groups for actuating the associated signal means responsive only to carrier current received through said medium during half cycles of said one polarity of 2s Seid Control voltages end-means infieachfef the fr: ceivers of the third and viourth Iof saidfgroupsor actuating the associatedsignalrneans responsive only to carrier current received throughsaid mereceivers in said second and Afourth groups `being tuned to respond only to carrier impulses received over said medium `at 'saidother impulse frequency.

16. In a telephonesystem, subscriber lines including party lines, aplur'alityvof subscriber stag for connecting calling and called lines, means for 'transmitting time coded impulses ojiringingcurrent of a particular frequency over 4one conductor of a called party line.y to ring certain ofthe stae i l5 tions connected to each of saidparty linesmeans tions on the line and for transmitting liketirne power line subscriber stations comprising carrier transmitting and receiving ineans for'r transmitting and receivingvoice and signalginodulated vcarrier currentover said Apower line, carrier terminal,v equipment connecting said power line to one of said party lines, and means including means `in said carrier terminal equipment and means at each of said power line stations for signaling certain of said power line stations when ringing current is received by said carrier terminal equipment over one condi1ctor of said one party line, and for ringing the other power. line stations When ringing k.Current is received by said carrier terminal equipment over tlievother con'- ductor of said one party line. e.

` ROBERT'C. EDSVON.

` LESTER HOCHGRAF.

k REFERENCES CITED V The following references are of record inthe le of'ths patent: l j

UNITED' vSTATES PATENTS ff Number "Name H Date, 2,108,909 i Vinent Feb. 22, 1938 2,164,033 Halliganl June 27, 1939 2,197,414 Plae v Apr. 16, 1940 2,294,905 IrIonaman Sept. 8, 1,942 2,302,544 Halligan Nov.f17,` 1942 2,378,326 Rees ,June'12,1945 2,408,299 Davis Sept. 24, 1946 2,430,471

Lang Nov. 11,1947 

